Purpose:
To determine the spatial characteristics and frequency of visual field (VF) deficits for VF loss produced by diabetic retinopathy and glaucoma in an evaluation of VF screening using a free iPad application, Visual Fields Easy at the Tilganga Institute of Ophthalmology, Kathmandu, Nepal.

Methods:
Visual field screening was performed using the Visual Fields Easy iPad app, which presents 88 Goldmann sIze V targets (22 per visual field quadrant) at a 16 dB intensity on a 31.5 apostilb (10 cd/m2) background. A red fixation point is presented at one corner of the display (located 33 cm in front of the observer) and test locations are presented (200 msec duration) at various locations in the quadrant and then the red fixation point moves to another corner of the display (the next quadrant). A 24-2 SITA Standard test procedure was also performed for comparison purposes. 210 normal control eyes, 183 eyes with glaucoma and 18 eyes with diabetic retinopathy were tested. We compared the number of missed points on the screening test with the number of locations outside normal limits for the SITA Standard 24-2 Total Deviation (TD) and Pattern Deviation (PD) probability plots.

Results:
The number of missed test locations for the Visual Fields Easy screening test demonstrated a good correlation (r=0.79) with the SITA Standard Mean Deviation (MD) and Pattern Standard Deviation (PSD) values (r= 0.60). The average testing time for the iPad VF screening test was 3 minutes and 18 seconds. For normal control subjects and diabetic retinopathy patients, there was no difference in the frequency of VF deficits in different quadrants. There were approximately twice as many locations outside normal limits for TD compared to the screening test, but PD abnormalities were similar to the screening results, indicating that mild deficits were not detected by the screening procedure. Similar findings were noted for the glaucoma eyes, except that the SITA Standard TD and PD results showed a slightly greater proportion of deficits for the nasal visual field while the screening procedure did not show this difference.

Conclusions:
The Visual Fields Easy procedure appears to be a relatively effective procedure to perform population screening of the visual field. The current findings provide a basis for developing platforms and probability values that can be used for refined adaptive screening procedures.